1. Field of the Invention
The present invention relates to a structural arrangement technique of a reducer, particularly to a speed reducer having a self-locking function and a compound type reducer device thereof.
2. Description of Related Art
In the structural arrangement technical field of conventional reducers, the self-locking function to be studied herein meant that driving power was loaded on an active member so as to generate forward output at a specific reduction ratio from a driven follower. When no driving power was loaded on the active member to be a free end, driving power (including a driving force exerted by an external power source, a driving force from torque generated by their gravity force of the follower and its connected members) was so loaded on the follower that it could not drive the active member of the free end to reversely rotate, i.e. the so-called “self-locking”. The “self-locking” meant a mechanism generated at a tooth flank between the active member and the engaged follower except of device arrangement (for example, a driven or reciprocating level, a positioning latch or a pin), such as, events latch, etc., manufacturing cost of which increased.
Conventional reducers generally included a mechanism having a worm wheel driven by a worm shaft, a planetary gear, and a spin-wave driver. Only the mechanism having a worm wheel driven by a worm shaft was designed by modification of engaging angle between tooth flank of the worm shaft and tooth flank of the worm wheel so as to achieve the above self-locking objective.
Please refer to FIGS. 1 and 2 which disclosed a schematic diagram showing an arrangement of conventional worm wheels and worm shafts and their lead angle. They demonstrated that a lead angle α was formed at an engaged a tooth flank between a general worm shaft 71 and a worm wheel 72. For the worm shaft 71, the lead angle α(the so-called friction angle) is formed by a slope formed from a worm shaft lead L and a worm shaft circumference length S. When the worm shaft 71 of the active member rotated, a positive force F was exerted from a tooth flank 71a of the worm shaft 71 onto a tooth flank 72a of the worm wheel 72 of the follower. A component force Fsinα generated in the clockwise direction of the lead angle α by using the positive force F was smaller than the friction force μ×Fcosα (μ is a frictional coefficient between the tooth flank 71a and the tooth flank 72a) generated at the tooth flanks 71a, 72a between the worm shaft 71 and the worm wheel 72, a self-locking effect was generated. In other words, at the state of self-locking design, a reverse rotation of the worm wheel 72 forced to reversely drive the worm shaft 71 because the tooth flank 71a and 72a was engaged. An advantage of the self-locking function is that every transmission component of the reducer mechanism was protected from un-predictable reverse rotation, thus, there should be no damages or risk.
In addition to the above mechanism of the worm shaft driving the worm wheel, there were no self-locking mechanism mounted on the conventional planetary gears and spin-wave driver till now. Conventional spin-wave drivers and planetary gears belong to typical speed reduction gearing devices. A spin-wave driver was a speed reduction gearing device. The first spin-wave driver invented was a Harmonic® driver disclosed in U.S. Pat. No. 2,906,143 filed in 1955 by C. W. Musser. After continuous improvement, details of a spin-wave driver mechanism were disclosed in U.S. Pat. No. 5,643,128.
In comparison to conventional planetary gears, conventional spin-wave drivers could provide more number of teeth on engaged gears and a larger amount of gear range, therefore, conventional spin-wave drivers provided better driving accuracy and driving efficiency regarding output value of the whole ratio of reduction.
Furthermore, in the conventional techniques, there were no wave-motions involved in the present invention. A similar wave-motion of the prior arts was the above spin-wave driver.
A general conventional spin-wave driver comprised a cam (or a so-called wave generator), a plurality of rollers and a spline wheel (having specific internally toothed circular spline wheel) from inside to outside. The cam was used as a input shaft. The plurality of rollers were arranged around a location between the cam and the spline wheel. A plurality of spline apertures which could accommodate rollers to engage were arranged on the spline wheel in ring-shaped form. The cam was used to drive some of the plurality of rollers by providing input force so as to engage the corresponding spline apertures of the spline wheel in order to rotate a bearing member at a ratio of reduction.
Furthermore, from the contents of the patents, it can be known that every spline aperture in the conventional spin-wave drivers comprises a tilting tooth flank extending along both sides of a void between the teeth and the tooth flank and the tooth flank at both sides extents and connects to a crest of teeth at both sides. The contour shape of each spline aperture is approximately V-shaped. Some of the rollers in the conventional spin-wave driving process would engage with tooth flank of the engaged spline aperture driven by a cam surface of the cam. Then, the tooth flank of the spline aperture was used as an effective contact surface for transmitting driving force of the rollers. For example, in U.S. Pat. No. 5,643,128, it was disclosed that a bearing member (roller ring) for receiving a plurality of rollers were arranged between the cam and the spline wheel. In some embodiments, the bearing member is used as an output shaft so as to drive the bearing member to rotate at a ratio of reduction by a force provided by rollers driven and transmitted by a driving force of the cam via transmission of the tooth flank of the spline aperture.
From the above descriptions, it could be known that not only the tooth flank of the spline apertures could be used as an effective contacting surface for transmitting working force, but also it could be used as an effective contacting surface for providing force to the rollers from the cam. We could observe that during the spin-wave driving process, when the cam surface pushed and drove the rollers to contact the tooth flank of the spline apertures, the driven rollers moved to a displacement at a radial direction regarding to the cam axis and to an angular displacement at an angular direction surrounding the cam axis. Then, the displacements would affect whether the tooth flank could be an effective contacting surface for sufficiently or really transmitting functional force and providing force generated by the cam. The conventional spin-wave drivers could maintain good driving accuracy and driving efficiency. However, in prior arts, the contour of the disclosed spline apertures is in V-shaped form. The well-known patents did not disclose or teach or study that the techniques of forming the contour of spline apertures and the cams were capable of effectively transmitting functional force, such as, when an input shaft rotated for half a circle, the rollers would move into a next position of the spline aperture. During the procedures, the speed would become uncertain because of an unclear definition of the V-shape so that the speed of the roller moving into the next spline aperture would become unstable. The driving accuracy of the conventional spin-wave drivers regarding output end under variation of tiny rotational angle would be affected.